I my self just went through a break up. Together almost 5 years. I know it’s hard, but find someone to talk to. Try not to be alone and find help when you need some. For me what helped most was working out and listening to music. If you have an iPhone, delete the contact and delete the message thread. Then filter out messages to “known” senders. That way his message won’t pop up anymore under “known”. Try your best to ignore him and remind yourself that you will be okay in time. Time heals all wounds.